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A279551
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Number of length n inversion sequences avoiding the patterns 000, 010, 110, and 120.
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22
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1, 1, 2, 4, 10, 27, 79, 247, 816, 2822, 10158, 37875, 145695, 576288, 2337412, 9698820, 41089107, 177424188, 779699793, 3482575169, 15791709187, 72621800171, 338388714955, 1596314968112, 7618218238583, 36756086159343, 179176803145900, 882002961543492
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OFFSET
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0,3
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COMMENTS
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A length n inversion sequence e_1e_2...e_n is a sequence of integers where 0 <= e_i <= i-1. The term a(n) counts those length n inversion sequences with no entries e_i, e_j, e_k (where i<j<k) such that e_i <= e_j and e_i >= e_k. This is the same as the set of length n inversion sequences avoiding 000, 010, 110, and 120.
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LINKS
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EXAMPLE
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For n=3, the inversion sequences are 001, 002, 011, 012.
For n=4, the inversion sequences are 0011, 0012, 0013, 0021, 0022, 0023, 0112, 0113, 0122, 0123.
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CROSSREFS
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Cf. A263777, A263778, A263779, A263780, A279552, A279553, A279554, A279555, A279556, A279557, A279558, A279559, A279560, A279561, A279562, A279563, A279564, A279565, A279566, A279567, A279568, A279569, A279570, A279571, A279572, A279573.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Typo in comment corrected and a(10)-a(27) added by Alois P. Heinz, Feb 22 2017
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STATUS
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approved
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